Page 7 - Volume 2, Issue 1, January 2009

Pesticide exposure risks

5

the German Model (Machera

et al.,

2009).

Data from the second greenhouse study

conducted with a handheld lance indicate

that potential dermal exposure measured

(75% percentile) was 12-13 times the value

estimated using the German Model (Mach-

era & Tsakirakis, pers. comm.).

Interpretation of data

Use of predictive models

Within the EUmost regulators use the UK

POEM or the German model. The UK model

is based mainly on local unpublished stud-

ies conducted mainly by industry and the

Government laboratories such as the Central

Science Laboratory. The predicted exposure

is expressed in mass or volume of the formu-

lation or the spray liquid per unit time (mg/h

or ml/h). Surrogate exposure levels are cho-

sen to be the 75th percentile values. An esti-

mated value for potential dermal and inha-

lation exposure is given based on the input

parameters, from which actual dermal ex-

posure is estimated, to give a final figure for

the systemically absorbed dose based on

default values for clothing penetration/per-

meation and dermal absorption. This value

is compared to the systemic Acceptable Op-

erator Exposure Level (AOEL) value for a par-

ticular compound.

In the UK model exposure during mixing

and loading is assumed to be confined to

the hands with respiratory exposure not tak-

en into account. The dermal exposure esti-

mation is based on the number of pesticide

containers or packs (operations) which the

worker has to deal with during one working

day. The estimation of operator exposure is

therefore based on the amount of active in-

gredient handled during mixing and load-

ing together with the exposure during the

application itself which is time rather than

mass dependant. The concentration of the

spray liquid but not the treated area is in-

cluded for the calculation of the exposure

during application.

The German model is based on the

amount of the pesticide handled during

one working day, and exposure level is ex-

pressed as units of mass per amount of a.i.

handled (mg/kg a.i.). The potential expo-

sure is calculated, including potential re-

spiratory exposure, for both mixing and

loading and application. Again the actual

exposure is calculated as the mass of pes-

ticide on the workers skin area after pene-

tration through clothing. The actual dermal

and inhalation exposure is then compared

with the AOEL value.

There is also a Dutch model which is a

literature-based model using international-

ly published studies. The units for exposure

values are similar to the UK model (ml/h or

mg/h), but the dermal exposure during mix-

ing and loading is not limited to the hands.

The potential exposure is calculated as for

other models; however the estimation of

the actual exposure is left to expert judge-

ment, and is often close to the potential ex-

posure (Kangas and Sihvonen 1996).

In the Dutchmodel, the estimation of the

operator exposure for outdoor applications

is based on the working time, the concen-

tration of the formulation and the concen-

tration of the spray liquid. This is supported

by an additional model for mixing and load-

ing based on field studies carried out in the

Netherlands. The exposure is dependent

on the amount of pesticide handled and is

expressed in mass units per amount of ac-

tive ingredient handled (mg/kg a.i.) as in the

German model.

A number of assumptions are made,

which often differ, in the different models,

such as the wearing of clothing, both the

workers own clothing and PPE, and the pen-

etration and permeation of PPE which is

worn. The rates of uptake from the skin also

vary as do the statistical parameters on sur-

rogate values used such as the geometric

mean used in the German model, the 75th

percentile in the UK POEM and the 90th per-

centile in the Dutch model.

The rate of coverall contamination is

one of the factors that determine the pro-

tective factor of the PPE worn during pesti-

cide application, representing the challenge

to the PPE. In an ideal scenario, the rate of